Many of the cleaning compositions heretofore recommended for use in connection with the cleaning of tableware have been subject to one or more significant disadvantages. Perhaps the paramount difficulty involved relates to the tendency of such compositions to leave undesirable spots and films on the washed tableware. As will be recognized, aesthetic considerations rather than purely functional criteria are often of overriding importance in regard to the suitability of a given cleaning composition, especially when contemplated for use in connection with the cleaning of tableware.
Further, environmental concerns have placed a premium on developing surfactants having increased biodegradability. Biodegradability is defined as that property possessed by a material enabling it to be decomposed by bacteria or other living organisms.
Ideally, surfactants utilized in the washing of tableware in automatic dishwashers will have a combination of biodegradablity characteristics and improved rinsing properties.
The prior art is replete with the disclosure of various surfactant compositions. By way of illustration, U.S. Pat. No. 3,956,401 discloses liquid surfactants having the formula: ##STR1## wherein R is a substantially linear hydrocarbon and more particularly an alkyl group having an average of from about 7 to about 10 carbon atoms; R' is a linear, alkyl hydrocarbon of from about 1 to about 4 carbon atoms; R" is a linear, alkyl hydrocarbon of from about 1 to about 4 carbon atoms; x is an integer of about 1 to about 6; y is an integer of about 4 to about 15; and z is an integer of about 4 to 25.
As another illustration, U.S. Pat. No. 4,925,587 discloses hydroxyalkyl polyethylene glycol and hydroxyalkyl polypropylene glycol ether surfactants corresponding to the following general formula: ##STR2## in which R.sup.1 is a linear C.sub.6 -C.sub.16 alkyl radical;
R.sup.2 is a linear or branched, saturated or unsaturated C.sub.1 -C.sub.22 alkyl radical; PA1 R.sub.3 is hydrogen or a methyl group; and n is a number of from 0 to 30.
As yet another example, U.S. Pat. No. 4,317,940 discloses biodegradable surfactants described as being useful as agricultural emulsifiers and having the following general formula: ##STR3## wherein R is a linear, alkyl hydrocarbon chain having an average of from about 6 to about 10 carbon atoms; R' is a linear, alkyl hydrocarbon of 1 to about 4 carbon atoms; R" is a linear, alkyl hydrocarbon of from about 1 to about 4 carbon atoms; x is an integer of from about 8 to about 12; y is an integer from about 19 to about 25; and z is an integer from about 2 to 7.
As still yet another illustration, U.S. Pat. No. 4,827,028 discloses the production of anionic surfactants by reacting an unsaturated dicarboxylic acid such as maleic acid or fumaric acid with at least one epoxy-capped poly(oxyalkylated) alcohol having the formula (A) and (B): ##STR4## wherein R is a hydrocarbon containing radical having from 1 to about 8 carbon atoms; R.sub.1 is a hydrocarbon containing radical having from about 6 to about 18 carbon atoms; x is an integer having a value from about 6 to about 40 and y is an integer having a value from about 8 to about 50. The ratio of x:y is from about 2:8 to about 8:2; and the mole ratio of dicarboxylic acid to epoxy-capped poly(oxylalkylated) alcohol is from about 1:1 to about 10:1.
The above-described surfactants typically have high caustic solubility, which can be an important surfactant characteristic. Unfortunately, an increased emphasis on biodegradability and surfactant cleaning performance in the cleaning of tableware, particularly when utilizing detergent compositions having low phosphate concentrations, has resulted in requirements which are not completely satisfied utilizing the compositions described in the above-referenced patents.